The biological pump transfers a significant amount of carbon dioxide to the deep ocean. The pump is driven by sinking aggregates of organic particles. The size, shape and structure of particles all influence the rates at which they sink and are remineralised, with fast sinking particles increasing the potential for long-term carbon storage. Transparent exopolymer particles (TEP) are sticky polysaccharides, which act as a biological glue. TEP are produced by certain types of phytoplankton and promote coagulation of phytoplankton cells to form aggregates [1]. There are several mechanisms by which TEP could promote aggregation, such as stickiness increasing the success rate of particle collisions. Turbulence in the upper water column has also recently been shown to enhance particle aggregation [2]. Turbulence may further promote TEP production in the upper-surface ocean which in turn may increase particle aggregation [3]. Climate change is predicted to suppress turbulence and alter phytoplankton community structure, which may impact TEP production [2], but these processes are not currently included in climate models. This project aims to combine an existing unique dataset, laboratory experiments and modelling to understand how TEP and turbulence impact aggregation with possible implications for the efficiency of the biological pump in the future.
The role of turbulence on TEP production and particle transformation in the upper ocean (0-200m) has not previously been explored using in situ observations. Initially, the student will analyse a novel cruise dataset (https://roses.ac.uk/custard/), which includes observations of turbulence, TEP and particle size profiles already collected at three different locations in the Southern Ocean. With this dataset we will test the hypothesis that sites with greater TEP concentration and/or turbulence will have a larger mean particle size, indicative of increased aggregation. With this as foundation, the student will be encouraged to choose the future direction of the project in line with their interests. There are several exciting avenues that could be explored which would be supported by the supervisors’ expertise. For example, further work could include experiments using a turbulence tank and the advanced digital imaging and laser diagnostic equipment available in the University of Southampton’s aeronautics group to explore hypotheses arising from the observational dataset, for example of how turbulence and TEP influences particle (dis)aggregation. A further possible route is for the student to use a simple biogeochemical model to test the influence of turbulence, TEP and particle morphology on particle fluxes and to explore wider consequences for the global carbon cycle.
The INSPIRE DTP programme provides comprehensive personal and professional development training alongside extensive opportunities for students to expand their multi-disciplinary outlook through interactions with a wide network of academic, research and industrial/policy partners. The student will be registered at the University of Southampton and hosted at the National Oceanography Centre, Southampton. Specific training will include:
Depending on the student’s interests, training in setting up experiments to measure particle movement in turbulent regimes could be provided, including image analysis techniques. Alternatively (or in addition), training to use and/or develop a computer model to simulate TEP, particle and turbulence interactions could be provided. This project will allow for a student to develop their computer programming skills, supported by the supervisors’ expertise. There will also be opportunities to participate on a sea-going research expedition to collect additional data and gain biogeochemical sampling and analysis experience. If within the interests of the student, a research visit to work with remote co-supervisor Dr Matthew Rau at The George Washington University (Washington D.C., USA) could also be arranged. The student will be encouraged to present their work at international conferences.
Please see https://inspire-dtp.ac.uk/how-apply for details.
[1] Engel et al., (2020) Marvelous Marine Microgels: On the Distribution and Impact of Gel-Like Particles in the Oceanic Water-Column, Frontiers in Marine Science, 7, 405, doi: 10.3389/fmars.2020.00405.
[2] Takeuchi et al., (2019) Turbulence mediates marine aggregate formation and destruction in the upper ocean, Nature Scientific Reports, 9, 16280, doi.org/10.1038/s41598-019-52470-5.
[3] Beauvais et al., (2006) Effects of turbulence on TEP dynamics under contrasting nutrient conditions: implications for aggregation and sedimentation processes, Marine Ecology Progress Series, 323, 47-57.
